The present invention relates to a device for producing metal fibers, especially steel fibers to be used in industrial floor, shotcrete, precast or structural applications.
Nowadays, the use of metal fibers for reinforcing concrete, especially for reinforcing floor plates having large surfaces, like e.g. industrial floor, or shotcretes, is widely known. These fibers are known in various embodiments. In most cases, such fibers comprise a substantially linear piece of wire with hook-shaped deformations on both ends, whereby the ends can be angularly or circularly deformed. Alternatively, the fibers can have an overall undulated form.
The metal fibers can be produced by forming a metal wire having a suitable thickness into the desired shape and by subsequently cutting pieces of the desired length of said shaped metal wire. Known devices for producing metal fibers accordingly comprise a forming assembly and a cutting assembly arranged in series.
The forming assembly comprises e.g. two oppositely and synchronously rotating forming rollers positioned one above the other, so that their respective outer circumferential surfaces are spaced at a distance substantially equal to the thickness of the metal wire. The circumferential surfaces of the two forming rollers comprise indentations and projections, whereby the projections of the first roller engage in the indentations of the second roller. The cutting assembly comprises e.g. a circular toothed cutter wheel, which cooperates with a fixed cutter block over which the metal wire is fed for shearing off said wire when one of the teeth of said cutter wheel passes in front of said cutter block.
During production, the forming assembly and the cutter assembly are each driven by a separate electric motor. The metal wire passes between the forming rollers, whereby the wire is shaped according to the rotational arrangement of said projections and indentations on the circumferential surfaces of the forming rollers. The shaped wire then passes into the cutter assembly. The electric motors of the forming and the cutting assembly are run synchronously, so that the cutter wheel cuts a fiber each time the appropriate portion of the shape is in a cutting position on the fixed cutter block.
A major disadvantage of such a device consists in the problem of synchronization of the electrical motors of the different assemblies. While synchronization of the motors works well enough at low production speed, problems arise if the production speed is raised above a certain value. This means that in practice, such a device is limited to a production speed below 7 m/s or even below 5 m/s.
The metal wire for producing the metal fibers is produced from wire rod in a dry or wet drawing process. Drawing machines achieve production rates of up to 50 m/s. Due to the limited production speed of the device for producing metal fibers, the drawn metal wire can not be immediately supplied to the device for producing metal fibers. Instead, the drawing machine winds the drawn metal wire onto a wire coil. A plurality of these wire coils are then mounted on an installation comprising several fiber production devices arranged in parallel, where the wire coils are unwound and the respective metal wires are shaped and the fibers are cut in parallel.
It is clear that the handling and the storing of wire coils is very labor-intense and space-consuming which leads to high production costs and hence to reduced productivity.
The object of the present invention is to provide an improved device for producing metal fibers, which allows a higher production speed.
In order to overcome the above-mentioned problem, the present invention provides a device for producing metal fibers from a metal wire, which comprises a forming assembly and a cutting assembly, said cutting assembly being arranged downstream of said forming assembly in the direction of production, said forming assembly being driven by driving means, wherein said cutting assembly is driven by said driving means and wherein said forming assembly and said cutting assembly are mechanically synchronized.
In the device according to the present invention, the forming assembly and the cutting assembly are driven by the same drive means. The synchronization of the two assemblies is implemented by a mechanical means, i.e. the two assemblies are subjected to a restricted guidance. This means that even at higher production speed, the synchronization is guaranteed and the two assemblies turn at the same velocity. Hence the production speed can be considerably raised compared to state of the art devices. It is thus possible to raise the production speed up to values above 30 m/s, i.e. up to values which are comparable to the production speed of the drawing machine. Accordingly the device for producing metal fibers can be mounted in series to the drawing machine and the drawn wire can be directly supplied from the drawing machine to the fiber-producing device without wasting productivity of the drawing machine. The temporary winding-up of the wire onto wire coils is no longer required and accordingly no more handling and storing of the coils is needed.
With the solution of the present invention, one single fiber-production device equals substantially the productivity of several state of the art devices arranged in parallel. This productivity is achieved without the need of large unwinders for up to ten wire coils. Considering further that no more storage room is needed for temporarily storing the wire coils between their production on the drawing machine and their unwinding in the fiber-production device, the proposed solution saves about 50% of the space needed for the entire installation. Furthermore no more handling of the coils is needed which reduces considerably the expenditure of work for the production of the fibers. It follows that the productivity of a fiber-production installation using a device according to the present invention is considerably increased compared to state of the art installations.
It has to be noted that the fiber-production device according to the present invention can be arranged in a very compact unit that is easily moveable. Hence it is possible at any time to remove the fiber-production device from the wire drawing machine. The wire drawing machine can therefore still be used for any other kind of wire production, e.g. by winding the produced wire onto wire coils for a different application. Furthermore the fiber production device can easily be replaced by an other device in case of excessive wear of the forming or cutting tools or in case that fiber having a different form should be produced.
In a preferred embodiment the device further comprises a feeding assembly, said feeding assembly being arranged upstream of said forming assembly in the direction of production and being driven by said driving means, wherein said feeding assembly and said forming assembly are mechanically synchronized. The feeding assembly preferably comprises at least one frictional roller, around which the drawn wire is winded in one or more wraps. Due to the friction between the roller and the drawn wire wrapped around the roller, the wire is entrained when said roller is rotationally driven. During fiber production, the frictional roller is driven at a predetermined velocity, which determines the rate of feed of the drawn wire. If the feeding assembly comprises two spaced apart frictional rollers connected in series, the drawn wire is preferably wrapped at least once around the outer periphery of the roller assembly. In this case, the straight wire portions between the two frictional rollers can equalize variations in wire tension caused by the preceding drawing machine. It follows that the forming assembly and the cutting assembly are independent from the variation in wire tension caused by the drawing machine.
In an alternative embodiment, the feeding assembly comprises two feeding rollers, which are arranged one above the other at a distance substantially equal to the diameter of the drawn wire. In this embodiment, at least one of the feeding rollers is driven at the required velocity.
The forming assembly and accordingly the cutting assembly are mechanically synchronized to said feeding assembly, so that their respective feeding rates correspond to the feeding rate of the feeding assembly. Neither the forming assembly nor the cutting assembly has to fulfill a feeding function and can hence be optimized for their respective forming or cutting function, resulting in an enhanced smoothness of production. Furthermore the forming assembly and the cutting assembly are independent from the variation in wire tension caused by the drawing machine.
In a preferred embodiment said cutting assembly comprises a cutting roller and a mating roller, said cutting roller comprising cutting elements extending radially outwardly of a circumferential surface of said cutting roller and said cutting elements being uniformly distributed over said circumferential surface. The cutting roller and the mating roller are advantageously arranged at a minimum distance one above the other, wherein one of said cutting roller and said mating roller is arranged above the traveling path of said wire and the other one is arranged below said travelling path. During fiber-production the wire passes substantially tangentially between said cutting and said mating roller, whereby the cutting elements are pressed into the wire and the wire is cut. It has to be noted that compared to the shearing operation of state of the art cutting devices, this cutting roller allows for a much smoother and softer cutting operation that does not disturb the normal feeding movement of the wire. Furthermore noise is considerably reduced.
In a preferred embodiment, at least one of said cutting roller and said mating roller is vertically moveable and the fiber production device comprises means for adjusting the vertical distance between said cutting roller and said mating roller. It is thus possible to adjust the vertical distance between the two rollers of said cutting assembly to the diameter of the wire to be processed. The adjusting means comprises e.g. an adjusting spindle or screw.
In order to adjust the cutting location of the cutting assembly to the accurate portion of the shape of said shaped wire, the cutting assembly is preferably displaceable in the direction of production, so that the distance between said forming assembly and said cutting assembly is adjustable. The cutting assembly can for instance be mounted on a slide, the longitudinal position of which is adjustable by an adjusting spindle. In this way, the location of the cutting position of the cutting tool can be exactly adjusted with respect to the forming assembly, so that the shaped wire is cut exactly in the right position of the shape.
It has to be noted that the mechanical synchronization between the different assemblies can comprise a belt drive and/or a gear drive and/or a chain drive.
The device of the present invention can be operated at production speed values above 30 m/s, i.e. at a production speed, where more than 2000 fibers are produced per second. This means that more than 2000 forming and cutting operations have to be performed per second. In order to raise the tool life of the forming or the cutting assembly at high-speed production, the fiber production device comprises advantageously means for imparting a to-and-fro movement to said wire in said cutting assembly and/or in said forming assembly, said to-and-fro movement in a horizontal direction transverse to a direction of fiber production.
It has to be noted that the diving means of the fiber-production device can be either a separate motor or the motor of the drawing machine. In the latter case, the synchronization of the feeding velocities of the drawing machine and the fiber-production device can be easily achieved by a similar mechanical synchronization. In other words, the fiber production device of the present invention can be advantageously combined with any possible pretreatment machine for the wire, as e.g. a preceding wire drawing machine or a wire rolling mill.
It will further be appreciated, that the device of the present invention can be used to produce fibers having any possible section, i.e. having a circular, oval or flat section.